"I have the same problem. I have two MS with the same 2.2 motor i have had one about a week before the the other one and the newer one is MUCH faster the the old one. why is that?"

my cars seemed to run a lot faster and longer when the NiCd battery was new. after a few days of use, they are run slower and dont last as long.

you could try swapping motors between the cars to see how much of the speed difference is due to the motors.